DE 10 2011 086 411 A1 discloses a method of the type in question for producing a piston of an internal combustion engine with a casting mould, in which a releasable casting core is placed and secured on supports of the casting mould. The casting mould is subsequently closed and a casting material introduced. Once the casting material has solidified, the casting mould is separated from the cast piston, wherein, after the piston is removed from the mould, at least one quill-type pin is removed, while at least one end portion remains cast in the piston and closes the cooling duct at this point. The dissolvable casting core itself is then dissolved in particular is rinsed out. By this means, in particular improved holding or securing of a casting core in the casting mould is intended to be able to be achieved.
DE 10 2012 215 543 A1 discloses a casting mould of a piston of an internal combustion engine with a soluble and substantially annular casting core for forming a cooling duct, and with at least two supports supporting said casting core during the casting operation. A panel element or closure element is arranged here at a connecting point between at least one of the two supports or an additional third support and the casting core, said panel element or closure element being at least partially fixedly connected to the piston after the casting operation and closing the connecting parts after removal of the casting core or forming an at least constricted intermediate outlet. The intention is thereby to be able to increase the stability of the casting mould and thus substantially simplify the handling thereof.
In previous methods for producing a piston, there has always been the problem, after the production of a piston blank of the piston, that, during the subsequent finish-machining chips or other dirt could under some circumstances enter the cooling duct and could no longer be removed from there with absolute certainty before the piston is put into operation in an internal combustion engine. It is true that the finish-machined pistons have also already to date been cleaned, under a high technical outlay, with up to 100 bar water pressure and, in the process, the cooling duct has been washed out, but, in this process, it could not absolutely reliably be ensured that the cooling duct was completely free of impurities, and therefore, for example, metal chips could be undesirably caught within the cooling duct. Impurities of this type remaining in the cooling duct may lead, however, during operation of the internal combustion engine, to malfunctions or in general to customer complaints regarding a required cleanliness of the components.